The typical rear wheel motorcycle suspension system of the prior art includes a rear wheel axle support which comprises two nearly equal metal swing arms held in nearly horizontal side-by-side relation; each of the swing arms being attached pivotally at their front ends to the motorcycle frame and at their rear ends to the motorcycle wheel axle so that the rear axle can move up and down in response to bumps. For further guidance and support the swing arms may be connected to one another by a bar or plate positioned near their center. The prior art motorcycle suspension systems further comprise either one or two shock absorbers surrounded exteriorly by a spring; the shock absorber and the spring being attached between the frame and the swing arms so as to damp upward motions of the swing arms caused by bumps thus controlling the rebound of the system.
These prior art suspension systems have several disadvantages. First, a spring will rebound past the initial displacement it experiences for large bumps thus amplifying the bump. Second, a coil spring will fatigue, eventually requiring that the suspension systems be disassembled and that the spring be replaced. Third, the springs and shock absorbers of the prior art are comparatively heavy and bulky adding weight to the motorcycle and making the suspension system more vulnerable to damage in an accident. Finally, it is almost impossible to achieve a continuous adjustment of the stiffness of the prior art suspension systems without disassembly.
Torsion bars are included in prior art suspension systems, but primarily in automobile suspension systems where they are connected directly to the control arms which hold the wheel spindel. Such systems are lightweight and do eliminate some of the above disadvantages but have difficulties in providing a rapid, smooth response to large displacements. The improved suspension system of this invention provides a better quality of ride despite large displacements.
It is an object of this invention to provide an improved suspension system for damping motions of the rear axle of the motorcycle which provides a progressively larger resistance to displacement as the size of the displacement increases without an unduly complicated mechanism, thus providing a smoother ride over a wider variety of surfaces.
It is another object of this invention to provide a progressively stiffer, but rapidly responsive, suspension system for a motorcycle which is ligher-in-weight and more compact than those of the prior art.
It is also an object of this invention to provide a suspension system for providing a gradually increasing resistance to increasing displacements of the motorcycle wheel which is more rapidly responsive to both large and small bumps than those of the prior art.
It is a further object of this invention to provide a simpler suspension system for providing a progressively stiffer ride which is continuously adjustable without requiring disassembly.